1. Field of the Invention
The present invention relates to a method of driving an ink jet recording apparatus.
2. Related Background Art
There are many types of ink jet recording apparatus. They are broadly classified into three types, i.e., (i) the continuous injection type (the continuous type), (ii) the impulse type (the on-demand type) and (iii) the electrostatic attraction type.
The continuous injection type is based on the principle that ink being continuously discharged is electrically charged and deflected to thereby accomplish recording, and therefore, apparatuses of this type are complicated and require collection of ink, a cleaning device, etc.
The electrostatic attraction type is relatively simple in structure, but is dangerous in requiring a high voltage and moreover, is very much limited in the ink must have special properties such as conductivity and poor in frequency responsiveness.
In contrast, the on-demand type is such that only when necessary, ink droplets are discharged by the pressure of a discharge energy generating element such as a piezo-electric element, and is very simple in structure. Therefore, great hopes are entertained for this type of recording apparatus.
Now, as regards the half-tone expressing method in recording apparatuses, there are conceivable two kinds of methods namely, a digital method such as the dither method and an analog method whereby the recording dot size is varied. However, in the digital half-tone expressing method, resolution must be sacrificed to increase the number of tones. For this reason, hopes are entertained for the analog recording method in which the recording dot size is varied to thereby control the recording density.
However, in the conventional ink jet recording apparatuses, it has been very difficult to control the amount of ink discharged. For example, in the continuous injection type, it is impossible to vary the amount of ink discharged. In the electrostatic attraction type, analog half-tone expression is possible, but it is difficult to increase the harmony range. Further, in the on-demand type, control of the amount of ink discharged is effected by varying the pulse voltage or pulse width applied to the piezo-electric element, but it has been difficult to make the harmony range greater by only the variation in the pulse wave-configuration.
For this reason, there are known an ink jet recording apparatus in which inks of different densities are properly used to thereby provide a great harmony range (Japanese Patent Laid-Open No. 102034/1978) and an ink jet recording apparatus in which a plurality of different nozzle diameters are provided to thereby provide a great harmony range. However, these methods cause the apparatuses to be generally bulky and complicated, and this in turn causes increased costs of the apparatuses.
On the other hand, it is known that the method as described in Japanese Patent Laid-Open No. 17589/1980 wherein the volume of an ink chamber is once increased to retract the so-called meniscus and thereafter ink is pressurized is not only more possible of discharging small ink droplets but also more excellent in frequency responsiveness than the method as described in Japanese Patent Publication No. 12138/1978 wherein ink is merely pressurized by a piezo-electric element to thereby cause ink droplets to be discharged.
However, after the discharge of ink from the orifice, the meniscus returns to the orifice while vibrating unstably as will later be described with reference to FIG. 4 of the accompanying drawings. Accordingly, if the viscosity and surface tension of ink are reduced when the temperature of the ink rises due to the rise of the environmental temperature and the heat generated by the continuous operation of the apparatus power source, motor, etc., the vibration will become more violent and thus, the apparatus will lack discharge stability.
The cause of such vibration is the reflected wave resulting from the pressure wave produced by the discharge pulse being repetitively repelled at the rear and fore ends of the nozzle, and the adverse influence of this reflected wave has been one of problems to be solved in ink jet recording apparatuses.